Fix: UST should not generate packet at destroy after stop
authorMathieu Desnoyers <mathieu.desnoyers@efficios.com>
Wed, 18 May 2016 18:04:11 +0000 (14:04 -0400)
committerJérémie Galarneau <jeremie.galarneau@efficios.com>
Thu, 19 May 2016 03:53:08 +0000 (23:53 -0400)
commit0dd01979d6f26886199ef746377640b57260421c
tree8e02644d1f68afece1af7b51cfa424cc130b75dd
parent0f6fd3631d4ef411b09f3136ca6929b31014d27e
Fix: UST should not generate packet at destroy after stop

In the following scenario:
- create, enable events (ust),
- start
- ...
- stop (await for data_pending to complete)
- destroy
- rm the trace directory

We would expect that the "rm" operation would not conflict with the
consumer daemon trying to output data into the trace files, since the
"stop" operation ensured that there was no data_pending.

However, the "destroy" operation currently generates an extra packet
after the data_pending check (the "on_stream_hangup"). This causes the
consumer daemon to try to perform trace file rotation concurrently with
the trace directory removal in the scenario above, which triggers
errors. The main reason why this empty packet is generated by "destroy"
is to deal with trace start/stop scenario which would otherwise generate
a completely empty stream.

Therefore, introduce the concept of a "quiescent stream". It is
initialized at false on stream creation (first packet is empty). When
tracing is started, it is set to false (for cases of start/stop/start).
When tracing is stopped, if the stream is not quiescent, perform a
"final" flush (which will generate an empty packet if the current packet
was empty), and set quiescent to true.  On "destroy" stream and on
application hangup: if the stream is not quiescent, perform a "final"
flush, and set the quiescent state to true.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
src/bin/lttng-sessiond/consumer.c
src/bin/lttng-sessiond/consumer.h
src/bin/lttng-sessiond/ust-app.c
src/common/consumer/consumer.h
src/common/sessiond-comm/sessiond-comm.h
src/common/ust-consumer/ust-consumer.c
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